Ready for Q-day: Denmark, Sweden and Poland to be connected by 1,240 kilometres of quantum-secure network
New project aims to strengthen Europe’s preparedness for the day when quantum computers become capable of breaking existing encryption methods.
What happens when quantum computers become powerful enough to break the encryption methods that currently protect our digital communication – from research data and financial information to communication in critical infrastructure?
This potential future scenario is popularly known as Q-day, and across Europe, authorities, researchers and other stakeholders are working to establish quantum-secure communication networks. These networks use quantum technology, among other things, for the secure exchange of the cryptographic keys that protect communication.
However, if the technology is to protect communication across Europe, it is not enough for each country to have its own network. National infrastructures must also be able to connect and operate across borders. This is the challenge at the heart of a new European project called QCI.dk-Cross Border (QCI.dk-CB).
Over the next three and a half years, the project partners will establish approximately 1,240 kilometres of quantum-secure communication infrastructure between Denmark, Sweden and Poland. The project brings together researchers, national research and education networks, public authorities and private-sector stakeholders from the three countries and is coordinated by DeiC.
“QCI.dk-CB is a unique project focusing on strong stakeholders including universities, authorities, private businesses and even the wider public. The overall aim is to tackle the data security challenges of the future. Together, the collaborators will apply the promising quantum technologies by creating and deploying an interoperable infrastructure quantum proof network strengthening soveringthy digitally across the EU member states”, says Martin Bech, Head of NREN and Coordinator of the QCI project.
Quantum-secure communication across borders
QCI.dk-Cross Border is part of the European Quantum Communication Infrastructure – EuroQCI – initiative, which aims to build a common network for quantum-secure communication across the EU. This will be achieved through national and cross-border terrestrial networks, which will eventually be complemented by satellite-based quantum communication. Denmark already participates in EuroQCI through the national QCI.DK project, which has established a quantum-secure network connecting a number of ministries and public authorities. With QCI.dk-Cross Border, the next step is to connect national networks across borders.
The network will use Quantum Key Distribution (QKD), among other technologies. QKD uses the properties of quantum physics for the secure exchange of cryptographic keys. In QCI.dk-Cross Border, QKD will be used over longer distances and across national networks.
The connections between Denmark, Sweden and Poland will include subsea fibre-optic cables. The project will also test how quantum signals can be transmitted through fibres that are simultaneously used for conventional data traffic.
"During the project lifecycle, we will use the new technology to establish resilient communication between the three countries to secure digital communication. Stakeholder mapping is a central part of the project, therefore, a use base as broad as possible will be engaged in the project, including the valuable feedback from the users and the community as such - as well as the wider public” Martin Bech
From land and sea to space
In the future, the European EuroQCI network will not only connect countries through fibre-optic cables on land and under the sea, but also via satellites, enabling quantum keys to be exchanged over greater distances.
QCI.dk-Cross Border will collaborate with NordicQCI, a parallel European project building quantum-secure connections between Sweden, Finland and Estonia. As part of NordicQCI, an optical ground station is being established in Stockholm – a telescope-based facility capable of transmitting and receiving optical signals between the ground and satellites. The ground station will be used, among other things, for communication with EAGLE-1, a European satellite developed to demonstrate Quantum Key Distribution from space.
DeiC coordinates the project
DeiC coordinates QCI.dk-Cross Border and is responsible for project management, quality assurance and overall project security. DeiC is also responsible for parts of the installation and operation of the network in Denmark and Sweden and leads the work to ensure that the infrastructure can continue to operate after the project ends.
Project period: 3.5 years from January 2026
Budget: EUR 10 million
Funding: The project has received funding from the European Union under Grant Agreement No. 101249191.
Coordinator: DTU-DeiC
Partners: Technical University of Denmark (DTU), including DTU Physics and DeiC; Swedish Research Council (SUNET); Poznan Supercomputing and Networking Center (PSNC); Koszalin University of Technology (KUT); European Spallation Source ERIC (ESS); and GlobalConnect as an associated partner.
Infrastructure: Approximately 1,240 kilometres of quantum-secure communication infrastructure between Denmark, Sweden and Poland.
Quantum Key Distribution (QKD) is a technology for securely exchanging the digital keys used to encrypt communication.
What makes QKD special is that the keys are exchanged using quantum signals. If someone attempts to intercept the signals while they are being transmitted, the signals are affected in a way that can be detected. The key can therefore be discarded if there are signs that someone has attempted to intercept it.
QKD does not encrypt the communication itself. Instead, it ensures that the keys used for encryption can be exchanged securely.